Abstract
A method of chromatographic separation of β-naphthol-3, 6-disulfonic acid (R acid) and -6, 8-disulfonic acid (G acid), in which cation exchange resin and cation exchange paper were used as a stationary phase and concentrated acidic salt solution as a developer, was investigated.
Studies on the adsorption behaviors of R and G acids on Amberlite CG-120 or Amberlite CG-50 in calcium chloride or sodium chloride solution showed that (1) in calcium chloride solution, the distribution coefficient (Kd) of these two acids became greater with increasing salt concentration, but in sodium chloride solution, the acids were not adsorbed, (2) the Kd of the acids was reduced with increasing pH value from 1.0 reaching minima at pH 4.04.5 and then became greater, (3) the rate of adsorption of the acids on Amberlite CG-120 was slow at room temperature (23°C) but was accelerated at 40°C, and (4) the separation factor of R and G acids on Amberlite CG-120 was larger than that on Amberlite CG-50.
The best separation was achieved with a peak resolution of 0.84 when a mixture was eluted at 41°C through a column of 17 mmgφ×700 mm of Amberlite CG-120 (200400 mesh) with 25 M calcium chloride solution of pH 2.9 at a flow rate of 0.37 ml/min. The acids in effluent were determined by u.v. spectrophotometry at 238.0 nm.
Moreover, the studies on paper salting-out chromatography using cation exchange paper showed that, when Amberlite WA-2 and Amberlite SA-2 were compared for the resolution of the isomers, the former gave a satisfactory result but the latter did not. The development (ascending) with 4M calcium chloride solution of pH 3.0 on Amberlite WA-2 gave the Rƒ values of 0.34 and 0.18 for R and G acids, respectively.
